Thursday, 14 February 2013

This week’s wow of the week! is a mystery rock that
I was sawing today. It is so interesting and unusual I thought it would be good
to share. The rock is a cementstone, with a complicated structure, as you can
see from the photo below. The bottom part consists of a conglomerate, with
clasts of cementstone in a black matrix that is packed with plant, shell and
fish fragments. The top part consists of bioturbated (burrowed) muddy sediment,
with no large fossils. The mystery is that in the bottom part are large calcite
spheres, with radial crystals growing into a void in the centre. These crystal
structures may be replacing gypsum, thin section analysis is needed to find
out, but all of them are spherical. I saw a similar structure in a sandstone
that occurred near to this cementstone (see photo). It might indicate that
gypsum grew in these rocks due to evaporation, but it also looks like the
spheres may have been transported in the conglomerate itself. Very unusual! Please
message me if you have seen this before and can give me any tips!

Top: the mystery rock, a cut section
through two of the spheres. Bottom: calcite spheres in a nearby sandstone.

What else has
been happening? Rock sawing/slicing/grinding/analysis continues…. And this week
I have started systematically sieving and picking through the samples I
collected in the field. I am very lucky to have a volunteer helping me, Tom
Worthington, a graduate from the University of Leicester, who is getting some
micropalaeontology work experience. With Tom’s help we can hopefully uncover
the hidden microfossils in hundreds of samples, and generate a lot of useful data.

News from
even smaller fossils is that the palynology work is well underway, with John
Marshall at the University of Southampton. With palynology we aim to date the
key tetrapod finds as well as build up a stratigraphic framework and further understand
environmental and climatic changes. In my next post I will update you on the
tetrapod finds discovered so far.

A quick advert
now for our local geology group seminar on Saturday 2nd March: We
are having a day of geological talks to celebrate the life work of Dr Trevor
Ford OBE, one of the founders of the Department of Geology at Leicester. The
talks range from Charnia fossils to
the geology of the Grand Canyon, everyone is welcome. For more information
visit the Charnia websiteor message me.